Cheatography
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H2 Chemistry Chemical Bonding
This is a draft cheat sheet. It is a work in progress and is not finished yet.
Physical Properties
Melting/ boiling point |
strength of bonding |
amount of energy required to overcome bond |
id-id< pd-pd< H-bond< (metallic/ ionic/ covalent) |
Solubility |
favourable bonds formed? |
bonds formed stronger than bonds broken |
| |
water + polar => ion-dipole |
polar + polar |
non-polar + non-polar |
Electrical conductivity |
presence of electrical carriers |
mobile delocalised e- or ions |
|
Covalent Compounds
covalent bonds |
EFoA between shared pair of e- and positively charged nuclei |
| |
dative covalent |
one atom contributes both bonding e- |
overlap or orbitals |
sigma (σ) bond |
head-on overlap |
s- and p-orbital |
| |
pi (π) bond |
side-on overlap |
p-orbitals only |
Strength = bond energy |
no of bonding e- (bond order) |
effectiveness of orbital overlap |
bond polarity (incr ionic character) |
| |
more bonding e- = stronger EFoA |
larger orbital = more diffused = less effective overlap |
more polar = stronger EFoA |
simple covalent structure |
simple discrete molecules |
| |
id id |
non-polar; weak |
size of electron cloud; polarisability |
| |
pd pd |
polar; stronger than id id |
strength of dipole moment |
| |
H bond |
H bonded to NOF + lone pair of electrons on NOF |
optimal ratio of H:e- (1:1) |
giant covalent structure: |
diamond |
each C bonded to 4 other C atoms |
giant covalent lattice |
graphite |
each C bonded to 3 other C atoms |
giant extensive planar layers |
weak id id between layers |
Molecular Shape and Arrangement
Valence shell electron repulsion theory |
VSEPR |
Conditions |
e- pairs arranged as far apart as possible |
minimise repulsion |
| |
LP-LP > |
LP-BP> |
BP-BP> |
BP- Lone e- |
| |
Repulsion of e- incr as electroneg incr |
electroneg incr = e- closer to central atom |
= stronger repulsion |
No of e- pairs |
e- pair geometry |
No of BP |
No of LP |
molecular geometry |
Bond angle |
2 |
linear |
2 |
0 |
linear |
180 |
3 |
trigonal planar |
3 |
0 |
trigonal planar |
120 |
| |
|
2 |
1 |
bent |
<120 |
4 |
tetrahedral |
4 |
0 |
tetrahedral |
109 |
| |
|
3 |
1 |
trigonal pyramidal |
107 |
| |
|
2 |
2 |
bent |
105 |
5 |
trigonal bipyramidal |
5 |
0 |
trigonal bipyramidal |
equatorial - 120; axial - 180 |
| |
|
4 |
1 |
see-saw (remove from equatorial plane) |
equatorial - <120; axial - 180 |
| |
|
3 |
2 |
T-shaped |
90 |
| |
|
2 |
3 |
linear |
180 |
6 |
octahedral |
6 |
0 |
octahedral |
90 |
| |
|
5 |
1 |
square pyramidal |
90 |
| |
|
4 |
2 |
square planar |
90 |
|
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Electronegativity
tendency of an atom to pull electrons towards itself |
nuclear charge |
stronger = greater pull |
| |
distance of e- from nucleus |
further = weaker pull |
trend |
down group |
decrease |
| |
across period |
increase |
Ionic compounds
Ionic bond |
IMFOA between oppositely charge ions |
structure |
giant ionic lattice structure |
strength |
lattice energy |
(product of charges)/(sum of ionic radius) |
coordination number |
number of opp-charged ions surrounding central ion |
ligand size increase, coordination number decrease |
IONIC vs COVALENT CHARACTER
Pure covalent |
Approx equal electroneg |
no distortion of electron cloud |
Covalent with ionic character |
atoms with electroneg diff |
dipole moment (δ+, δ-) |
incr electroneg diff = incr dipole |
Ionic with covalent character |
polarisation distorts anion e- cloud |
stronger polarising power of cation (charge density) |
= increase distortion = increase covalent character |
| |
some form of e- sharing |
larger e- cloud = incr polarisability |
= increase distortion = increase covalent character |
Pure ionic character |
complete transfer of e- |
e- cloud remains intact and spherical |
Metallic compounds
Metallic bond |
EFoA between metallic cations and sea of delocalised, mobile e- |
| |
in giant metallic lattice structure |
Factors affecting strength |
Charge density |
No of e- delocalised per atom |
Unique physical properties |
Malleable (beat into sheets) |
Ductile (drawn into wire) |
orderly arrangement of cation |
| |
Alloy formation |
non-metal atoms disrupts orderly arrangement |
tensile strength increase |
| |
Reflectivity |
Delocalised e- absorb light and excited |
promoted to higher level |
| |
|
De-excitation => release E |
=> light |
Special Cases
Anomalous Mr of organic acid in gaseous phase/benzene solvent |
Apparent Mr twice of anomalous Mr |
dimerisation |
either achieve octet, or due to favourable bonds formed (release E) |
Different physical properties of structural isomers |
1,2-nitrophenol has lower BP than 1,4-nitrophenol |
1,2-nitrophenol has intramolecular H-bond |
less extensive inter-molecular H bond |
Bp of HI> HBr>HCl |
incr in id-id down group |
decrease dipole moment down group |
incr id-id more significant |
Density of water > ice |
ice - hexagonal arrangement of water |
large amount of empty spaces |
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